Pressure sensitive diaphragms with stress
null zone oriented bridge patterns



Dec. 7, 1965 c. K. sTr-:DMAN Re- 25,924

PRESSURE SENSITIVE DI APHRAGMS WITH STRESS NULL ZONE ORIENTED BRIDGEPATTERNS Original Filed Aug. 25, 1961 5 Sheets-Sheet 2 mm am@ A rrens/5v5' Dec. 7, C Kv EDMAN Re. w

PRESS l SENSITIVE D APHRAGMS WITH STRESS NU ZONE ORIENTE!) BRIDGEPATTERNS Miginn Filer] Aug.. 25, 1961 5 Sheets-Sheet A r faim/5&6'

Dec. 7, 1965 K. STEDMAN Re. 25,924

PRESSURE SE TIVE PHRAGMS WITH STRESS LL ZONE ORIEN BRIDGE PATTERNSOriginal Filed Aug. 1961 5 Sheets-Sheet 4 Bgm@ (A A rra@ y' Dec. 7, 1965c. K. STEDMAN Re. 25,924

INHSSURE SENSITIVE DIAPHRAGMS WITH STRESS NULL ZONE ORIENTED BRIDGEPATTERNS Original Filed Aug. 25, 1961 5 Sheets-Sheet .E

ggz/z.

IN VEN TOR. f-cm S'rfDM/M/ @Nm AW United States Patent O 134,070, Aug.25, 1961. Application for reissue Oct. 22, 1964, Ser. No. 420,470

51 Claims. (CL338-2) Matter enclosed in heavy brackets appears in theoriginal patent but forms no part of this reissue specification; matterprinted in italics indicates the additions made by reissue.

The present invention relates to pressure sensitive assemblies, alsoknown as transducers, of the type in which the transduction meanscomprises a bridge pattern in the form of an integral lm or the likebonded to a flexible diaphragm, with strain sensitive change inelectrical resistance of the active segments of the bridge patternproviding an indication of magnitude of pressure exerted on thediaphragm.

More particularly, the present invention relates to pressure responsivetransducer assembles employing a exible diaphragm having thereon abonded bridge pattern in the form of an integral film or the like;wherein the bridge pattern comprises a plurality of active segmentsinterconnected at juncture areas in turn having relatively lowresistance conductor segments extending beyond the restrained edge ofthe diaphragm, the arrangement of said pattern being such that each ofsaid juncture areas lies substantially in the radial stress null zone ofthe diaphragm, with one active segment connected to each juncture areadisposed near-center from said null zone and with the other activesegment connected to said juncture area disposed near-edge from saidnull zone, and wherein such near-edge active segment is advantageouslydisposed so that a major part thereof is in the area of and [outside]near-edge with respect to the tangential stress null zone of saiddiaphragm. In certain preferred forms of the bridge pattern the activesegments thereof are composed of an electroconductive material having asubstantial transverse gage factor (Gt), and the active segments areoriented to advantageously utilize such transverse gage factor andthereby increase bridge sensitivity, the arrangement of such near-edgeactive segment being with a substantial part thereof disposed outside ofthe tangential stress null zone of the diaphragm and extending parallelto the restrained edge thereof, so that the bridge material insubstantial part responds to radial stress in relation to its transversegage factor and in susbtantial part responds to tangential stress inrelation to its parallel gage factor with such responses augmenting eachother.

In certain of its aspects, other advantages and characteristics of theinvention pertain to simple, durable and reliable arrangements of thebridge pattern to integrally include conductor film or like segments inturn having conductor output leads connected thereto, the pressuresensitive diaphragm of the assembly having a backing plate bondedthereto near the edge of the diaphragm, the conductor segments extendingfrom the active segments to annularly oriented positions externally ofthe backing plate, such conductor output leads being attached as bysoldering to the conductor segments, with the junctions beingencapsulated in means bonding the diaphragm and backing plate together.

Other aspects of the present invention involve the presentation ofseveral modified forms and variations of bridge patterns characteristicof the invention, and tech- Re. 25,924 Reissued Dec. 7, 1965 "ice niquesfor fabricating the bridge films, as well as techniques for assembliestransducer assemblies comprising such bridge tilms. Specific aspects ofthe invention also pertain to suitable electroconductive materials andsuitable orientation of active bridge segments on a diaphragm in orderto realize to greatest advantage the increase in sensitivity resultingfrom the transverse gage factors characteristic of certain materials.

As used herein, the terms active segments" and active film segmentsrefer to those portions of the bridge film pattern comprising theso-called arms or legs of an electrical bridge, which reect substantialchange in electrical resistance responsive to change in stress, i.e.those segments which are resistively active in performing the measuringfunction of the device. By the terms conductor segments and conductorfilm segments are meant those relatively low resistance segments of thebridge pattern connectively associated with the active segmentsinternally of the assembly and terminating externally of the diaphragm,serving as input and output connection points or juncture areas for theactive segments. By the terms conductor output leads and output leadsare meant the wire or like means connected to such conductor lm segmentsexternally of the diaphragm and lead externally of the assembly, bymeans of which leads the voltage input and variable output of the activesegments are electrically transmitted to externally associated measuringequipemnt.

By the term parallel gage factor, or GW is meant the sensitivity of thefilm or like material to change in electrical resistance resulting fromthe stress or component stress exerted parallel to or in the directionof current ow. By the term transverse gage factor, or Gm is meant thesensitivity of the bridge material to change in electrical resistanceresulting from the stress or component of stress exerted perpendicularlyor transversely to the direction of current flow.

By the term radial stress null zone is meant the annular zone of thediaphragm in which no substantial radial stress occurs upon tlexure ofthe diaphragm, i.e. the zone wherein the factor r/a minus the factorsubstantially equals zero. By the term tangential stress null zone ismeant the annular zone of the diaphragm wherein no substantialtangential stress occurs upon flexure of the diaphragm, i.e, the zonewherein the factor r/a minus the factor nel le m +3 substantially equalszero.

By the term lm or the like, as applied to the form of brideg patternmaterial, is meant material in the form of a thin sheet of uniformthickness dimension throughout, which thickness dimension is less byseveral orders of magnitude than the dimension of the diaphragm. By theterms integral film and integrally formed film, are meant a film ofhomogeneous nature throughout, comprising no soldered or like discreteconnection of separately formed segments,

As is known, when an edge restrained flexible diaphragm is subjected todifferential pressure at the faces, the diaphragm is loaded to be incompression in certain areas and directions and to be in tension inother areas and directions. Compound stresses occur such that portionsof the diaphragm are under substantial radial and/or tangential tensilestress and other portions of the diaphragm are under substantial radialand/or tangential compression stress. By the terms radial stress or S,.,and relative radial stress," or "Sr, are meant the physical stressesexerted on the diaphragm and bridge pattern which are exerted in adirection radially of the center of the diaphragm. By the termtangential stress, or Sg and "relative tangential stress, or SL aremeant stresses exerted in a direction parallel to the restrained edge ofthe diaphragm. Considering the stresses as they occur in relation to thecenter and restrained edge of the diaphragm, a given condition ofloading and diaphragm exure causes either compression or tension stressrelatively near the center of the diaphragm and either tension orcompression stress relatively near the edge of the diaphragm, dependingup the direction of flcxure. The hereinafter discussed considerations,as to the relation of stresses exerted in various regions of thediaphragm expressed in terms of the distance/radius ("r.f"a") ratio,[assuming] assume for simplicity that the direction of flcxure is towardthe side of the diaphragm on which the bridge film pattern is arranged,i.e. [assuming] assume the condition where the bridge in its unear-center regions is under tension and in its near-edge regions isunder compression, with the tensile stresses being denoted negative" andthe compression stresses being denoted positive However, as will beapparent, the principles here involved are equally applicable to theconverse situation where the bridge in its near-center regions is undercompression and in its near-edge regions is under tension, in whichsituation the stress factors (as in FIG. l) are oi the same absolutevalue but of opposite sign.

Giving due consideration to bridge pattern designs which optimallyutilize both radial and transverse types of stresses, and also utilizeboth the parallel gage factor and transverse gage factor of certaineleetroconduetive materials in order to attain optimum bridgesensitivity, minimize heating effects. and preferably provide that thebridge is internally self-balancing, are basic objects and features ofthe invention.

The bridge segments are integrally formed as by vapor deposition, to bethe same composition and thickness throughout so that all portionsthereof have the same responsiveness to temperature changes and toaging. Preferably, each active bridge segment has about the samelength/width ratio as the other active segment or segments, to beinternally balanced with electrically equal bridge arms. Also, eachactive film segment has a substantial area and is as long aspracticable, consistent with other design factors, in order that theheat generated in the segment be dissipated over a substantial area. Atleast two and preferably four active segments are employed, one segmentor opposed pair of segments being relatively near the center of thediaphragm and the other segment or opposed pair of segments beingrelatively close to the restrained edge of the diaphragm so that onesegment or pair is under compression while the other segment or pair isunder tension. However, use of four active segments is preferable formaximum sensitivity, with one opposed pair positioned on tensionedregions of the diaphragm and the other opposed pair positioned incompressed regions of the diaphragm, so as to provide a line pattern inthe form of a loop in which all the segments electrically augment eachother when connected as a Wheatstone bridge. In such an arrangementinvolving four active lm segments, the segments are quadrantly related,with one opposite pair of the segments disposed symmetrically of eachother so as to be subjected to substantially the same stresses, whilethe other opposite pair is likewise symmetrically oriented with respectto each other so as to be also subjected to substantially the samestresses. In order to minimize internal heating effects, and consistentwith the foregoing considerations, it is another characteristic of thefilm bridge patterns of the present invention that the active segmentsare each spread over a substantial area (i.e. as a film), yet are spaceda substantial distance from each other.

In preferred forms of the bridge lm pattern as herein disclosed, thearrangement of active segments comprises two oppositely disposed activesegments situated near the center of the diaphragm and two oppositelydisposed active segments situated near the restrained edge of thediaphragm, in conjunction with integrally formed, relatively lowresistance conductor segments, all of similar configuration andorientation on the diaphragm. This is accomplished most practicably bymaking the active segments and conductor segments of the same materialand same thickness. This integration of the conductor segments with theactive segment serves the advantage of eliminating any necessity forseparate output lead connections within the restrained edge of thediaphragm, with consequent constructional simplification. Suchconstructional simplification also avoids the problem of internalconnections being a limiting factor in the minimum size capability ofthe transducer. The integration of active and conductor segments alsoavoids the sometimes troublesome problem of bridge balance variationscaused by the presence of soldered connections at the bridge armterminals.

Two opposed conductor segments serve to transmit the voltage input tothe bridge loop, and the other two opposed conductor segments serve totransmit the bridge output voltage or signal to the output leads.

Still other features and advantages characteristic of the presentinvention include the utilization of a bridge film pattern formed toinclude integral, low resistance conductor segments extending to theperiphery of the diaphragm, with the film conductor segments bonded tothe diaphragm and with the backing plate also bonded to the diaphragm,and with the bonding means between the periphrey of the diaphragm andthe outer portion of the backing plate serving to encapsulate leadconnections to said conductor film segments, such manner of constructionand assembly providing that the assembly is construetionally rugged andelectrically insulated.

The bridge pattern mounting diaphragm is preferably but not necessarilycircular in form, and is edge restrained as by the clamping action of abacking plate bonded to the diaphragm. In the simplest case, a circulardiaphragm is clamped near its periphery and uniformly loaded across thediaphragm, as in the diaphragm of a pressure gage, for example. Thereverse or obverse surfaces of the diaphragm, or both surfaces, cancarry a bridge film pattern bonded thereon. When the diaphragm is ofitself electrically conductive, as when formed from metal, such isinsulated from the bridge film pattern by providing an insulating layerof bonding material therebetween. However, the diaphragm may of itselfbe an insulating material, such as silica, in which event the bridgepattern can be bonded directly to the diaphragm and the segmentsinsulated from each other by the diaphragm.

In order to more full describe certain features and advantages of theinvention, consideration will be given to the gage factors of the filmmaterial and to the relationship between the gage factors and bridgeoutput, i.e. bridge sensivity.

The gage factor G of an electroconductive material is defined as theratio of the fractional change of resistance, AR

and the fractional elongation l i.e.

m A1 n T The output voltage AV expressed as a fraction of the appliedvoltage V depends upon the combined iR R of the bridge arms;specifically All V equals one-quarter of the sum of the values of AR Rfor the four bridge arms.

The potential across the output depends on the potential establishedacross the input, and it is thus desirable that the active film segmentscomposing the bridge be of sufficiently high resistance to permitapplication of a relatively high potential across the input of thebridge without excessive current flow. In typical examples, theresistance R of each active lm segment of the bridge is about G-2000ohms.

The value of the gage factor G as defined by the above equation isdifferent [if] when the direction of current flow is parallel to thestrain Al/l than when the elongation is exerted in a directionperpendicular to, i.e. transverse to, the direction of current flow. Inother words, rather than a single gage factor G, there are actually twogage factors involved. These gage factors may be represented by thesymbols Gp and Gt. As will be apparent, in the situation where a bridgearm is subjected to strain in directions both parallel and perpendicularto the direction of current flow, then the resulting is the sum of thevalues that would result from either strain acting separately.Recognition of this distinction between the two gage factors Gp and G,is important because electroconductive materials vary considerably as tothe values of Gp and Gt, and unless the relative contributions thereofare taken into account in orienting the active film segments in relationto the radial arid tangential stresses, less than full utilization ofthe internal change in resistivity and loss in overall sensitivity ofthe bridge result. The signficance of the interrelation of the radialand tangential stresses and the parallel and transverse gage factors Ggand G, are developed more specifically hereinafter.

In order to obtain a maximum output per volt input to the bridge, it isdesirable to maximize the valve of for each segment. Studies incident tothe present invention indicate that the value of is dependent upon ther/a position and direction of the segments on the diaphragm and alsoupon the gage factors Gp and Gt, as above indicated. These parametersinfluence the pattern of the arrangement of the bridge segments in theideal case. However, at least for small diaphragms, where the segmentsare relatively close together, it is often necessary to compromisebetween the desired to minimize heating effects of the bridge currentand the desired to maximize the valve of of each bridge segment.

T he above objects and features incident to the development oftransducer assemblies and particularly the development of bridgepatterns therein with optimal utilization of both parallel andtransverse gage factors, as well as minimization of heating effects, andas well as internally self-balanced bridge networks, will be apparentfrom the following description, together with the accompanying drawings,wherein like numerals refer to like parts, and wherein:

FIG. 1 is a graphical presentation of the distribution of radial andtangential stresses occurring in a typical edge restained circulardiaphragm under uniform 1oad ing, which graphical presentation serves toshow some of the governing principles and consideration as to locatingthe active film segments on a diaphragm in accordance with the presentinvention;

FIG. 2 is a plan view of the exposed face of a typical bridge patternaccording to the present invention, showing its orientation with respectto the diaphragm on which it is bonded;

FIG. 3 is a view in diametric cross section through a transducerassembly employing a bridge pattern configuration such as shown at FIG.2.

FIGS. 4, 5, 6, 7 and 8 are views similar to that of FIG. 2, illustratingmodified forms of bridge patterns characteristic of the invention;

FIGS. 9, 10 and l1 are cross sectional views similar to the view of FIG.3, showing further variations of transducer arrangements according tothe invention;

FIG. 12 is a View in vertical cross section illustrating a typicalassembly mechanism for fabricating transducer assemblies according tothe invention;

FIG. 13 is a fragmentary view on a somewhat enlarged scale of themechanism shown in FIG. 12, further illustrating the backing plateclamping arrangement thereof, and taken substantially along line 13-13thereof;

FIG. 14 is a further view of a fragmentary nature of the mechanism shownin FIG. l2, showing the relation of elements with the diaphragm andbacking plate assembled; and

FIG. 15 is a view similar to FIG. 14 of a modified form of assemblymechanism, wherein the backing plate and diaphragm are assembled inreverse positions, as compared with the assembly procedure of FIG. 14.

In order to realize the basic principles and advantages of theinvention, an analysis of the forces exerted upon the active filmsegments and the changes in resistance resulting from such forces isnext presented.

In the following analysis, the diaphragm is assumed to be circular, edgerestrained and loaded uniformly across its face to generate compressiveand tensile stresses across the face of the diaphragm. In this respect,and while the following discussion refers to simultaneously occurringcompression in certain regions while tension occurs in other regions, itwill be understood that loading of the diaphragmn in the reversedirection is governed by the same principles, except that in suchreverse condition the areas of tension become areas of compression andthe areas of compression become areas of tension.

With the uniform loading of the diaphragm within the range of magnitudesuch that all parts of the diaphragm are displaced linearly, i.e. indirect proportion to the applied load, the distribution of stresses onthe diaphragm is given by the following equations:

where Sr is the radial stress at any point at a distance r measuredalong the radius a from the center; St is the tangential stress, i.e.,the stress perpendicular to the radius at the above point; W is theload; t is the thickness of the diaphragm; a is the radius of thediaphragm to the clamped edge; and rn is the reciprocal of Poissonsratio (l/m) for the material of the diaphragm.

The [positive] negative sign indicates that the stress is a tensilestress, and the [negative] positive sign that the stress is acompressive stress.

Values for a silica diaphragm from the above table are plotted on FIG.1, in which the upper plot (designated radial stress") indicates thevalues of Sr for a silica diaphragm of n1 value of about 7.1 and thelower curve (designated "tangential stress,) indicates the value of S',for the same diaphragm as a function of the distance-fromcenter ("r/a)at which the stresses are evaluated.

The values presented by FIG. 1 are indicative of the actual stresses inany diaphragm because the factor has a constant value K for any givendiaphragm. Also, with diaphragms of various sizes and materials, thefactor K has a different magnitude but the shapes of the curvescorresponding to those of FIG. l change very little, i.e. the radialstress null zone and tangential stress null zone occur in all instancesat r/a values of about 0.6 and about 0.9, respectively, regardless ofthe diaphragm size and diaphragm material.

For any value of K the radial stress becomes zero at a value of r suchthat (maril 1/2 .filles/wi) (3) The radical stress is positive in[tension] compression, ie., when r (m-l-l) 1/2 5 sm+1 (4) and it isnegative in [compression] tension, i.e. when r (m-l-l) l2 a. (g3n1ll)(d) The tangential stress is zero when r (m-HA) U2 'tt-[(m-l-3) optimumsensitivity, regions of the diaphragm are selected for adjacent activesegments of the bridge which provide stress factors of opposite sign,i.e. where one segment of the bridge is stressed in tension, a region ischosen for the one or more active segments connected to it which isstressed in compression. Thus, for example, one active segment ispositioned as close to the restrained edge of the diaphragm aspracticable (i.e. near-edge" of the diaphragm), and the active segmentor segments connected to it are positioned so as to be as close to thecenter of the diaphragm as practicable (i.e. near-center" of thediaphragm).

For reasons which will appear from the graphical presentation of FIG. l,the active segments are most advan tageously comprised of a materialhaving a substantial transverse gage factor Gt as well as a parallelgage factor Gp, and at least one of the active film segments is locatedto take advantage of the tangential gage factor. Thus, for example,those active segments which lie relatively close to the restrained edgeof the diaphragm are oriented so that preferably at least about 20% ofthe total change in the resistivity `of the segments occurs as a resuitof the relatively large radial stress in this area across the segment(noting the radial stress curve of FIG. 1 at values of r/a approaching1.0) which radial stress is responded to in a manner at least primarilydetermined by the transverse gage factor Gt of the segment. In otherwords, in certain of the bridge pattern designs here presented, theactive segment or segments which lie near the restrained edge of thediaphragm have a configuration so that a considerable an-d preferablypredominant portion of their length extends tangentially of, i.e.parallel to, the restrained edge. By this arrangement, the non-opposingtangential stress near the restrained edge is utilized, as well as thechange in resistance reflected by the high radial stress. Also, thebridge pattern is considerably simplilied to the extent that theeffective length of the near-edge segment or segments of a bridgepattern can readily be of about the same overall length as thenear-center segment or segments thereof, with the no-strain resistance(R) of the bridge pattern segments being substantially equal. It isimportant to be able to keep the near-edge bridge segments relativelyshort in bridge pattern design, in that if unduly long such near-edgesegment or segments must be arranged with a multiplicity of reversebends and must have segment portions positioned relatively closely toone another, with adverse heating etlects.

With respect to the near-center segment or segments of a bridge pattern,it will be noted from FIG. 1, that the magnitude of the tangentialstress and the magnitude of the radial stress are much more similarbeing substantially equal at the center of the diaphragm, with thetangential stress however being substantially greater in the regionextending from ncar-center to the radial stress null zone. For thisreason, it has also been found advantageous to orient the near-centersegment or segments to extend substantially parallel to the restrainededge, but not critically so, in which location the parallel gage factorof the film material responds to the tangential stress and thetransverse gage factor of the material responds to the radial stresswhen the film material has a substantial transverse gage factor.

The closer a near-edge active segment is to the restrained edge of thediaphragm, the higher will be the value of the radial and tangentialstresses. However, practically speaking, a neareedge segment can includeportions which have a radial or chordal as wel] as tangentialorientation, to increase the overall length and area of the segment andthus reduce localized heating. On the other hand, for the near-centersegment or segments, the closer such are located to the center of thediaphragm, the greater the value of the radial and tangential stresses.However, heating effects and the desirability of having the near-centersegments of about the same length/width ratio as the near-edge segmentsintroduce compromise considerations so that as a practical matter thenear-center segments are placed in the region Where r/a values are about0.35 to 0.6. As earlier indicated, it is desirable to not only attain amaximizing of the value but also to obtain active film segments ofsufficient area to distribute the heating effect. Accordingly, selectionof the segment orientations, whether radial, arcuate, chordal, orcombinations thereof, will depend upon the Gp and Gc gage factors of thematerial, the overall length of the segments desired, the placement ofsegments to minimize heating, and the contribution of the r/a placementas retlected by the comparative tangential stress and radial stressinvolved.

In the specilic bridge patterns herein disclosed, both of the near-edgesegments are of relatively the same configuration and are symmetricallyspaced about the diaphragm center. Similarly, the near-center segmentsare in turn of the same configuration relative to one another and aresymmetrically spaced from the center.

The nlm bridge pattern shown in FIG. 2 comprises an opposed pair ofactive film segments 20 and 22, of equal length and Width, andsymmetrically spaced from the center 24 of the diaphragm 26 in a chordalnear-center disposition. The active film segments of the bridge pat ternshown in FIG. 2 also comprise a second opposed pair of segments 28 and30 which are primarily arcuate and situated in near-edge disposition,i.e. adjacent to the clamped or restrained edge of diaphragm 26, theclamp line being indicated in FIG. l at 32. The junction of therespective pairs of opposed bridge film segments 20, 22, 28 and 3i) arejoined by output connector segments 34, 36, 38 and 40 which extend fromthe respective juncture areas 34', 36', 38 and 4d' to the peripheraledge 26' oi the diaphragm in each instance, and are integrally formedwith but considerably wider in dimension than the active film segments20, 22, 28, 30 to provide relatively low resistance. Said outputconductor segments 34, 36, 38, 40 in their peripheral portions are eachsoldered to a respective output lead 42, 44, 46 and 48, the respectivesolder area in cach instance being indicated at 50, S2, 54 and 56.

The clamped or restrained edge 32 of the diaphragm as illustrated at FG.2 is established by mounting of thc diaphragm 26 on a backing plate 58(FIG. 3) by means of an adhesive ring 6d providing a bond between thep0rtions of the diaphragm lying under line 32 and an inset or groove 62provided adjacent to the edge of said backing ring SS. As shown in FIG.3, said backing plate 58 optionally includes a boss or stop portion 58'centrally contiguous of diaphragm 26, which stop portion 58' serves tolimit the extent of movement of the diaphragm 26 and prevent accidentalbreakage thereof in the event of application of excessive pressure.

Bonding ol the diaphragm 26 and backing plate 58 is preferably but notnecessarily augmented by a ring of encapsulating resin 64 encirclingbacking plate 58 and adhering to it as well as the peripheral area ofdiaphragm 26 lying between the outer edge 66 of the backing plate 58 andthe peripheral edge 26' of the diaphragm 26. Such outer bonding ring 64encapsulates and effectively insulates as well as physically strengthensthe respective connections 50, 52, 54 and 56 between respective outputconductor segments 34, 36, 38, 40 and output leads 42, 44, 46, 4S.

In the illustration of the diaphragm provided by FIG. 3 (and also inFIGS. 9-11 discussed below), the thickness dimension of the bridge filmpattern is necessarily eX- aggerated for illustration purposes. Inactuality, the thickness of the bridge film pattern in a typicaltransducer assembly is suitably on the order of 100 angstroms.

The bridge film pattern configuration shown at FIG. 2

is suitable for use where the film material has not only a substantialparallel gage factor Gp but also a substantial transverse gage factorGt, so as to permit the tangential stresses to make a significantcontribution to the change in resistance of the active film segments.Active film segments 20, 22 are of relatively equal length, equallyspaced about both sides but relatively near the center 24 of thediaphragm, while the active film segments 28, 30 are similarly ofrelatively equal length and lie close to the clamped edge 32 of thediaphragm.

Characteristic of the invention, the near-edge active film segments 28,30 in the pattern shown at FIG. 2 are disposed to lie primarily quitenear the clamped edge 32 of the diaphragm 26, and extend arcuatelytherealong except for relatively short chordal sections 28', 30'connecting the arcuate sections of segments 28 with juncture arcas 34',36', 38', 40.

Relating the bridge pattern configuration shown at FIG. 2 to the stressrelationships graphically presented at FIG. 1, it will be seen that thenear-edge film segments 28, 30, including the short chordal portions28', 30' thereof, are of a radial distance from the center 24 so thatthese segments lie entirely in regions of the diaphragm 26 where the r/avalues are greater than (In-l-l) W i (3n1ll) As shown by FIG. 1, thiscorresponds to values of r/a of greater than about 0.6, and theplacement of said near-segments 28, 30 is such that such lie entirely inthe area of diaphragm 26 where the r/a ratio is greater than about 0.6.More specilically, juncture areas 34', 36', 38', 40', are placed to fallat points where the value of r/a is about 0.7, and the arcuate sectionsof the segments 28 are placed so that the center lines thereof fall atan r/a value greater than about 0.9, e.g. a value of about 0.95. It willbe seen from FIG. l, that the radial stress factor in and outside of thetangential stress null zone is quite high and the tangential stress iseither about zero or is of the same sign, i.e. augments or at least doesnot oppose the radial stress. With the disposition of such arcuatesections of segments 28, 30 to be parallel to the restrained edge 32,the parallel gage factor Gp of the film material is related to thetangential stress, and the perpendicular gage factor Gt of the materialis related to the radial stress, with the AR sensitivity primarilyresponding in a manner determined by the Gt of the film material. If thematerial making up the bridge pattern had no transverse gage factor Gt,it will be observed that very little change in resistance of lm segments28, 30 would occur in response to change in stress. By use of a materialhaving a substantial transverse gage factor, however, and placement ofat least the primary part of the active film segments 28, 30 near therestrained edge of the diaphragm, the high radial stress factor isutilized to good advantage, and tangential stress opposition or loss isalso avoided so that optimal sensitivity resuits.

The nearcenter film segments 20, 22, in the bridge pattern shown in FIG.2, lie along chords which are geometrically aligned with segmentportions 28', 30'. With respect to the desired placement of saidnear-center segments 20, 22, the closer these are to center 24 of thediaphragm, the greater the negative value of AR/R (again note FIG. l).However, it is also important to not place the near-center segments 20,22 too near each other, because of adverse heating effects. For thisreason, the near-center segments 20, 22 are placed to be not less thanabout an r/a value of about 0.35 distance from the center 24 of thediaphragm. With the chordal configuration of the near-center segments20, 22, as shown at FIG. 2, such lie entirely within a region where thevalue of r/a is substantially less than [i (1n-H) (Suhl-1) lll i.e. lessthan about 0.6. In this area, and again noting FIG. l, it will be seenthat the radial stress factor and tangential stress factor are bothnegative and therefore `augment one another without certain portions ofthe segments introducing opposition or loss from the point of view ofsensitivity to change in resistance resulting from changes in stress.Also, with respect to the configuration of said near-center segments 20,22, it is to be observed from FIG. l that although the magnitude of thetangential stress is a greater negative value, the magnitude of both thetangential and radial stress are substantial so that while an optimumnear-center segment configuration lies substantially parallel to therestrained edge 32 (noting the bridge patterns presented by FIGS. 5-8 inthis respect) such is not necessarily the case; for example the chordalsegment 20, 22 can provide adequate sensitivity to change in resistance.

FIG. 4 illustrates a slightly modified variation of the bridge tilmpattern shown at FIG. 2, in which the chordal section 28a', 30a' of thenear-edge Segments 28a, 30a are directed radially of center 24 of thediaphragm 26. This configuration substantially increases the length ofthe arcuate portions of segments 28a, 30a, and also to some extent thelength of radial portions 28a', 30a'.

FIG. illustrates a bridge pattern configuration in which the near-edgefilm segments are primarily radially directed, with each such Iilmsegment having two radially directed segment portions. As shown at FIG.5, the upper near-edge film segment comprises radially directed segmentportions 70 joined by a relatively low resistance connector portion 72,and the lower near-edge film segment comprises radially directedportions 74 joined by relatively low resistance connector portion 76.Also, in the bridge configuration shown at FIG. 5, the near-centersegments 78, 80 are of arcuate configuration and because of their closerplacement to center 24 of diaphragm 26 are shorter in length than thecorresponding segments 20, 22 of the bridge configurations shown byFIGS. 2 and 4. The type of bridge film pattern shown in FIG. 5 has itsjuncture areas 34', 36', 3S', 40' in the radial stress null zone of thediaphragm 26, and is particularly adapted for use of a bridge materialhaving no substantial transverse gage factor, e.g. Nichrome, in that itsnearedge segments are radially oriented to respond to the high radialstress in the near-edge region of the diaphragm. Also, where adequatesensitivity in resistance can be obtained by comparatively short segmentlengths, the bridge configuration shown at FIG. 5 is advantageous fromthe point of View of the physical separation of each active lilm segmentor segment portion from the others.

FIG. 6 is a variation of the bridge pattern shown by FIG.5, in which thenear-edge active segments 70a and 74a are made shorter and increased innumber, as compared with segment portions 70, 74 of FIG. 5, such segmentportions 70a, 74a being respectively connected in series by means ofrelatively low resistance, arcuately extending connectors 72a and 76a.By this variations, the radially extending, near-edge segment portions70a, 74a are increased in total effective length, if desired, whilestill retaining an orientation in the region of the diaphragm having anr/a value greater than about 0.6.

FIG. 7 illustrates yet another variation of bridge configurationcharacteristic of the invention, wherein each near-edge segment isformed of a plurality of respective segment portions 82 and 84 formingsmall acute angles with radii of the diaphragm, which chord Segmentportions 82, 84 are joined by respective short, arcuately extendingsegment portions 86 and 88 lying nearest the restrained edge of thediaphragm, and also joined by respective arcuately extending, relativelylow resistance connectors 90 and 92 lying relatively near the respectivejuncture areas 34', 40' vand 36', 38'. Also, in keeping with the greatereffective length of the near-edge bridge segments 82, 86 and 84, 88, thearcuately extending, nearcenter bridge segments 94 and 96 of the bridgeconfiguration shown at FIG. 7 are comparatively longer than thecorresponding near-center segments 78, 80 of the coniigurations shown atFIGS. 5 and 6.

FIG. 8 serves to illustrate a further type of variation in bridgepattern configuration, wherein the juncture areas terminating the activefilm segments in the radial streSs null zone are brought to thc edge ofthe diaphragm separately. Selecting the configuration of active segmentsof the bridge pattern of FIG. 7 to serve `to illustrate this type ofvariation, the bridge pattern shown at FIG. 8 splits the outputconductor segments 34, 36, 38, 44) of the FIG. 7 configuration intorespective output conductor segments 34a and 34b, 36a and 36h, 38a and38h, and a and 40h. By this arrangement, the near-edge bridge segments32, S6 connects only to juncture arcas 34a' and 40h', near-edge bridgesegment 34, 33 connects only to juncture areas 36h' and 38a',near-center bridge segment 94 connects only to juncture areas 38h' and40a', and near-center bridge segments 96 connect only to juncture areas34h and 36a'. To complete the output connections, and by analogy to theoutput connection of arrangement shown with respect to the bridgepattern of FIG. 2, the output conductor segments 34a, Mb, 36a, 36h, 38a,331, 40a and 49h are each soldered to respective output leads 42a, 42h,44a, 44h, 46a, 46h, 48a and 48h, the respective solder area in eachinstance being indicated at a, 50h, 52a, 52h, 54a, 54h, 56a and 56h.

Should such be desired, the bridge contiguration of FIG. 8 enables theuse externally of the transducer of temperature compensating and trimresistors such as conventionally used in electrically balancing aWheatstone bridge. While it is an advantage and preferable objective ofthe bridge configurations of the present invention to provide that suchare internally resistively balanced, it will be understood that a degreeof external balancing may at times be desired, and FIG. 8 serves to showin this respect that the bridge patterns of the invention readily havethis capability.

FIGS. 9, l0, and l1 illustrate certain typical variations with respectto the malte-up of transducer assemblies cornprising an edge restraineddiaphragm 26, i.e. certain modiiications of the transducer assemblyearlier discussed with respect to FIG. 3. Thus, in FIG. 9, the diaphragm26 with its film pattern 20, 22, 36, 40 can be bonded by aclhesive ringand encapsulating ring 64 to a relatively rigid backing plate 58a havinga centrally provided bore 100 in communication with pressure tube 102,by means of which tluid of a pressure to be measured is introduced intothe interspace between diaphragm 26 and backing plate 58a. With sucharrangement, the transducer becomes a differential pressure gage,sensitive to the difference in pressures established between theinncrtace and outerface of the diaphragm 26.

The transducer construction shown at FIG. l0 shows another variation inbacking plate detail, its backing plate 58h being cut away along aninner surface 104 to provide a larger internal chamber between diaphragm26 and the backing plate 58h and permit greater ilcxural displacement ofsaid diaphragm 26.

FIG. l1 illustrates a further variation as to backing plateconfiguration of a transducer assembly comprising a diaphragm 26,wherein the backing plate 58e is attached to diaphragm 26 by theencapsulating ring 64, and wherein the backing plate 58e is of athickness substantially equal to the thickness of diaphragm 26. As willbe understood, the forms of backing plates 58h and 58e as shown at FIGS.l() and ll, being of substantially equal thickness as diaphragm 26, areof themselves flexed materially under pressure and will thereforeaugment the pressure responsiveness of the diaphragm 26. It isoftentimes quite practical to malte the diaphragm and backing plate ofthe same material and thickness, so as to have substantially similartiexural characteristics in both.

The diaphragm can be of metal, such as steel, or can be of non-metallicmaterial, such as quartz, fused silica,

glass, plastic or ceramic material, and the backing plate likewise canbe of any suitable metallic or non-metallic material with strengthproperties comparable to or greater than those of the diaphragm.

A highly useful application of the invention is in connection withminiaturized transducers, with the bridge hlm pattern applied to adiaphragm of insulating material, preferably silica. The silicadiaphragm is considered particularly advantageous by virtue of itsinherently good temperature stability and good physical characteristics,With low mechanical hysteresis, with small variation of modulus ofelasticity which change in temperature, and with a low coeicient ofexpansion.

With respect to the bridge pattern, such is bonded on the surface of thediaphragm either by gliie or other insulating bonding agent, in the caseof metallic diaphragms, or directly on the diaphragm, in the case ofelectrically non-conductive diaphragm materials. The deposition of thebridge film material on the diaphragm or, on an insulating layer bondingsame to the diaphragm, can be by any of several well-known techniques,and the bridge pattern can be developed by any of several well-knowncircuit methods as, for example, by painting, drawing, silk-screeningand photo-engraving. Various techniques for such purpose have beendeveloped, as indicated; see, for example, National Bureau of StandardsCircular 468, entitled Printed Circuit Techniques, National Bureau ofStandards Project 0602-11-3583, and National Bureau of Standards Report5139. See also Preliminary Survey of Electrical Strain Characteristicsof Evaporation Films, by Krusky and Parker, February 1957, published bythe Office of Scientific Publications, National Bureau of Standards. Seealso British Patent 689,785.

As for the composition of the material from which the bridge filmpatterns is formed, such is to be electroconductive with substantial butrelatively low order rcsistance (eg. on the order of U-200() ohms peractive segment), and is preferably a semi-conductive material exhibitinga substantial transverse gage factor as well as a :substantial parallelgage factor, i.e. a material such as silicon or germanium alloys, andsuch as certain metallic resinatcs. As will be understood, manyelectroconductive materials compositions has a substantial transversegage factor. The gage factors characteristic of any givenelectroconductive material can be readily ascertained by test. However,by way of certain typical examples, it was found that a film of an alloyof .Si-75% Cr on glass exhibited a Gp of 2.1 and a G, of 1.3. A film ofan alloy of 75% Si-2S% Cr on glass demonstrated a Gl, of 1.5 and a G, of-.54. Some precious metal resinaies have proven to be quite satisfactoryfor purposes of being utilized as the film material according to thepresent in vention; for exampie palladium rcsinate marketed under theproprietary term Liquid Bright Palladium #4334 by Hanovia Liquid GoldDivision of Engelhard Industries, exhibited a parallel gage factor ofabout 2.0 and a transverse gage factor of about 0.83. Metallic palladiumevaporated onto silicone resin demonstrated a Gp of 0.84 and a Gt Of Asshown by certain of the above examples it is a characteristic propertyof certain electroconductive ninterials that an inverse relation existsbetween the parallel gage factor Gp and the transverse gage factor Gt,i.e. the Gp of the material is a positive factor and the Gt of thematerial a negative factor. With such a material, place ment of thenear-edge active segments in the region be tween the radial stress nullzone and the tangential stress null zone results in the radial stressresponse in the nearedge augmenting the tangential stress responsethereof, in that while the stress factors are of opposite sign in thisarea of (cf. FIG. 1) the gage factors are also of opposite sign with theresult that the change in resistance of the segment with change instress is relatively increased.

As will also be understood, certain adaptations of the principles of theinvention can employ only part of the features thereof. Thus, when thefilm material selected for a particular' transducei design has nosubstantial transverse gage factor, design advantages still pertain tothe orientation of the active segment juncture areas at about the radialstress null zone with one or more segments near-center and one or moresegments near-edge of the diaphragm, but without especial orientation toutilize segment layout to provide substantial cross segment stresses(such as in the bridge pattern presented by FIGS. S and 6 for example).ln these types of bridge pattern arrangements, for example, it will beunderstood that the bridge pattern material can be any electroconductivematerial with a substantial parallel gage factor, such as Nichrome,manganin oi` constantin, or can be carbonloaded paints orelectroconductive plastic tape.

In laying the bridge material on one or both sides of the diaphragm, ithas been found preferable to use a vacuum vapor deposit technique, sincethe resulting film is quite uniform in thickness throughout andtemperature coefficient characteristics are also quite uniform in allportions of the film.

Any suitable technique can be used for vacuum deposition of the film ofelcctroconductive material onto the diaphragm, such as disclosed in thetext entitled "Vacutim Deposition of Thin Films, by L. Holland, publ. byWiley and Sons (1958), for example.

The thickness of the film can suitably be about 1GO-50() Angstrom units,for example.

With such electroconductive film coating formed on the surface of thediaphragm, the bridge film pattern can be developed by any of severalsuitable means, such as by a photo-engraving process wherein the film isfirst coated with a photo resist, then irradiated with visible orultra-violet light from the side upon which the pattern is to bedeveloped, through a positive mask ofthe pattern to be produced on thediaphragm. Such procedure irradiates all portions of the photo resist inthe pattern. The exposed diaphragm film is then developed by washing inWater or other solution to remove the unexposed photo resist, leavingthe resist in the form of the desired pattern on the surface of thediaphragm.

In some instances, in forming the pattern in the deposited filmmaterial, the film material can prove rather difficult to remove byconventional electrolytic etching. In such situation, another suitablemethod of forming the tilni pattern is that of stylus etching. In thisprocedure, the film material is connected to the positive side of abattery, and a porous stylus is used, such as for example a chisel-endwood stylus saturated with an electrolyte, with the stylus connected tothe negative pole of the battery. The stylus is simply guided over thefilm material not coated with photo resist to form the pattern byremoval of the unwanted material. Alternately, with respect to thepattern formation, a cloth saturated with an electrolyte may bestretched over and spaced somewhat from the film material carryingdeveloped resist. With the film material connected to the positive poleof a battery and with a wire rod connected to the negative pole of thebattery, the wire rod is rolled across the cloth and the exposedportions of the film are removed. Any suitable electrolyte may beemployed. For example, when the film material is a Si-Cr alloy, a dilutesolution of NaOH suffices.

Transducers according to the present invention can be assembled with aninternal pressure which is substantially atmospheric, orsuperatmospheric, as desired, or can be assembled to that the internalchamber pressure is subtantially a vacuum.

Typical assembly techniques for transducers according to the presentinvention, will be considered in connection with FGS. 12-15. As shown inFIG. l2, the assembly equipment can comprise a base supporting, as bylegs 13.2, a support plate 114 having a cut away portion liti in itsupper face to receive diaphragm 26 after the bridge pattern has beenformed thereon. Said support plate 114 is suitably heated in the area ofthe diaphragm plate, as by an electric heating coil, schematicallyindicated at 118. Upstanding from support plate 114 are a plurality ofguide rods 120 which serve to maintain a reciproeable slide plate 122parallel to the face of sup port plate 114. Said slide plate 122 issuitably raised and lowered by means of a press rod 124 threaded thereinand passing through stuffing box 126 in cover 128 which in turn isattached as by bolts 130 to base 110. Cover seals 132 are also providedbetween cover 128 and base 110, and tube 134 permits the pressure insidethe cover to be maintained at any desired value while the transducer isbeing formed. lf a vacuum is desired, for example, then the interior ofthe assembly equipment is maintained evacuated during the assemblyprocedure.

Slide plate 122 is circularly recessed as at 136 (FIG. 13) to receivethe backing plate 28, and a slide block 138 with an adjustment bolt 140are provided to clamp the backing plate 28 in proper position in slideplate 122.

With the diaphragm 26 and backing plate 58 in proper positions onrespective support plates 114 and slide plate 122, the annular groove 62of the backing plate is filled with a pre-formed adhesive ring 60, theslide plate 122 is placed on guide rods 120, the cover installed, andthe desired assembly pressure is established. Then, diaphragm 26 havingbeen iplaced on and heated by the heating means 118 in the meanwhile,the slide plate 122 is moved down under slight pressure so that firmcontact is maintained between diaphragm 26 and backing plate 28 whilethe adhesive ring 60 in groove 62 sets (cf. FIG. 14). The assembleddiaphragm and backing plate are then removed from the assemblyequipment, the output leads are soldered to the output connectorsegments (e.g. in FIG. 2), and the encapsulating ring 64 is applied andcured to complete the transducer assembly.

FIG. illustrates a variation in assembly procedure, suitable for usewhen the chamber between the diaphragm and the backing plate is notvacuurnized. This assembly equipment as shown in FIG. l5, is quitesimilar to but construetionally simpler than that of FIGS. 12-14.Backing plate 58 is supported on a smooth base plate 1l4a, with thediaphragm 26 placed thereon after a ring of preformed thermosettingadhesive 60 is placed in groove 62. Then, a smooth surface slide plate122s, suitably heated as by the electric heating coil 118a, is broughtdown in pressure contact with the diaphragm 26 and maintained in suchposition until the ring 60 sets.

From the foregoing discussion of the basic principles governing thepresent invention, as Well as the typical embodiments thereof presented,various other modifications, adaptations and features thereof will occurto those skilled in the art to which the invention is addressed, withinthe scope of the following claims.

What is claimed is:

l. A pressure responsive device comprising [an edge restrained diaphragmhaving an] a diaphragm and means restraining the edge of said diaphragm,said diaphragm having an electrically non-conductive surface t0 which ishonden' an integral bridge pattern with a plurality of active segments`interconnected {at} h v juncture areas in turn having connected theretorelatively low resistance conductor segments [extending beyond therestrained edge of the diaphragm]; said juncture areas lyingsubstantially in the radial stress null zone of the diaphragm, with oneactive segment connected to each juncture area disposed near-center fromsaid radial stress null zone of said dinphragm and the other activesegment connected therto disposed nearedge from said radial stress nullzone of .mid diaphragm.

2. A pressure responsive device according to claim l, where in a majorpart of the active segment disposed [outside] near-edge of said radialstress null zone is disposed in the area of and [outside] near-edge withrespect to the tangential stress null zone of said diaphragm.

3. A pressure responsive device according to Claim 1, wherein saidbridge pattern is composed of a material having a substantial transversegage factor as well as a substantial parallel gage factor; saidnear-edge active segment having a substantial part thereof disposed[outside of] near-edge with respect to the tangential stress null zoneof the diaphragm and extending parallel to the restrained edge thcreof,so that the bridge material in substantial part responds to radialstress in relation to its transverse gage factor and in substantial partresponds to tangential stress in relation to its parallel gage factor,with such responses augmenting each other.

4. A pressure responsive device according to claim l, wherein saidbridge pattern is composed of a thin, integrally deposited film ofelectroconductive material.

5. A pressure responsive device according to claim 1, wherein saidbridge pattern is composed of a thin, integrally formed film ofelectroconductive material having a substantial transverse gage factoras well as a substantial parallel gage factor.

6. A pressure responsive device according to claim 5, wherein said tilmpattern is formed of an electroconductive material having a substantialtransverse gage factor, selected from the group consisting oisiliconchrome alloys and metallic resinates.

7. A pressure responsive device according to claim l, wherein saiddiaphragm is non-metallic and electrically non-conductive.

8. A pressure responsive device according to claim 7, wherein saiddiaphragm is fused silica.

9. A pressure responsive device according to claim 1, wherein saiddiaphragm is metallic and the bridge pattern segments are electricallyinsulated therefrom.

10. A pressure responsive device comprising a diaphragm, meansrestraining the edge of said diaphragm, said diaphragm having anelectrically non-conductive .surface with an integral bridge patternbonded thereto, said Epridgc] bridge pattern arrangement comprising atleast one active segment near the center of the diaphragm, substantiallyentirely in the region thereof where the dis tance/radius ratio is fromabout 0.35 to about 0.6, and at least one other active segment disposedsubstantially entirely in the region where the distance/radius ratio isat least about 0.7.

11. A pressure responsive device comprising a diaphragm, meansrestraining the edge of said diaphragm, said diaphragm having anelectrically non-conductive surface with nn integral bridge patternbonded thereto, said bridge pattern arrangement comprising at least oneactive segment near the center of the diaphragm substantially entirelyin the region thereof where the distance/radius ratio is from about 0.35to about 0.60, and at least one other active segment disposed near theedge of said diaphragm, substantially entirely in the region where thedistance/radius ratio is at least about 0.7, such latter active segmentbeing predominantly in and [outside of] near-edge with respect to theregion of said diaphragm where the distance/radius ratio is about 0.9.

1?.. A pressure responsive device according to claim 1l, where in saidbridge pattern pattern is composed of an electroconductive materialhaving a substantial transverse igage factor as well as a substantialparallel gage factor.

13. A pressure responsive device according to claim 12, wherein saiddiaphragm is fused silica.

14. A pressure responsive device according to claim 13, wherein saidelectroconductive material is an integrally deposited film ofsemiconductor material.

15. [in a] A pressure responsive device comprising a diaphragm withnicnas restraining the edge thereof and with nn electricallynon-conductive surface having bonded thereto a strain sensitive bridgepattern with active segments consisting of an integrally formedelectroconductive material having a substantial transverse gage factoras well as a [longitudinal] parallel gage factor, said bridge patternhaving active segments arranged on said diaphragm to be substantiallyresponsive to strain both perpendicular and parallel to the direction ofcurrent flow therein.

16. A pressure responsive device according to claim 15, wherein at leastone of said bridge pattern active segments is arranged to provide thatat least 20% of the total change of resistance thereof occurs fromresponsive to strain perpendicular to the direction of current How.

17. A pressure responsive device according to claim 15, wherein thebridge pattern is comprised to a vacuum deposited tilm ofelectroconductive material having a substantial transverse gage factor.

18. A `pressure responsive device according to claim 17, wherein saidfilm pattern is formed of an electroconductive material having asubstantial transverse gage factor, selected from the group consistingof silicon-chrome alloys and metallic resinates` 19. A pressureresponsive device according to claim 15, wherein said diaphragm is afused silica wafer.

20. [ln a] A wafer type pressure responsive device comprising [an edge`clamped diaphragm] a diaphragm, means restraining the edge of saiddiaphragm, the said diaphragm having an electrically non-conductivesurface with an integral film pattern bonded [to said diaphragm] theretoedge-to-edge [and in essentially quadrant arrangement], f the diaphragm,said film pattern having two diametrically opposite active film segmentsdisposed symmetrically near the center of said diaphragm, and two otherdiumetrically opposite active film segments disposed near the [clamped]restrained edge of said diaphragm, said active film segments terminatingin juncture areas substantially at the radial stress null zone of thediaphragm, the thickness of all such active film segments beingsubstantially the same and the length/width ratio of each film segmentbeing substantially equal to the length/width ratio of the other activefilm segments so as to be internally `balanced resistively and so as tobe internally temperature compensated, and all of such resistor filmsegments being spaced substantially one from another so as to minimizeheating effects.

21. A pressure responsive device according to cl-aim 2li, wherein saidactive film segments are composed of an electroconductive materialhaving a substantial transverse gage factor as well as a parallel gagefactor, and the active film segments near the center of the diaphragmextend at least primarily circumferentially thereof to longitudinallyreceive tangential diaphragm stress and transversely rcceive radialdiaphragm stress, the active film segments situated near the [clamped]restrained edge of the diaphragm being arranged in a pattern withsubstantial clomponents thereof extending both tangentially and radiallyto be sensitive to both tangential and radial stress.

22. A pressure responsive device according to claim 21, wherein saidfilm pattern is formed of an electroconductive material having asubstantial transverse gage factor, selected from the group consistingof silicon-chrome alloys and metallic resinates.

23. A `pressure responsive device according to claim 20, wherein saiddiaphragm is a fused silica wafer.

24. A [wafer type] pressure responsive assembly, comprising a pressuresensitive diaphragm having an electrically non-conductive surface, andan electro-conductive film pattern on said [diaphragm] surface, with atleast one active segment situated near-center of said diaphragm, and atleast one active segment situated near-edge of said diaphragm and withrelatively low resistance conductor segments integral with and extendingfrom juncture areas [as] at the ends of said active segments [to theperiphery of said diaphragml, the said assembly further com prising abacking plate annularly bonded to said diaphragm only near the peripheryof said diaphragm, said backing plate being overlapped by portions ofsaid conductor film segmcntsl 25. An assembly according to claim 24,wherein said backing plate is substantially more rigid than saiddiaphragm.

26. An assembly according to claim 24, wherein said diaphragm and saidbacking plate are formed ofthe same material.

27. An assembly according to claim 24, wherein said diaphragm and saidbacking plate are of substantially the same thickness and consequentlyhave similar flexural characteristics, the flexure `of the backing platethus augmenting the pressure responsive fiexural characteristics of saiddiaphragm.

28 An assembly according to claim 27, wherein said diaphragm and saidbacking plate are fused silica.

29. An assembly according to claim 27, wherein said diaphragm and saidbacking plate are metal.

30. A [wafer type] pressure responsive assembly, comprising a pressuresensitive diaphragm an electrically nonconductire surface on saiddiaphragm, and an integrally formed electroconductive film pattern onsaid [diaphragm] surface with at least one active segment situatednear-center of said diaphragm and at least one active segment situatednear-edge of said diaphragm, and with relatively low resistanceconductor segments integral with and extending from juncture areas atthe ends of said active segments to the periphery of said diaphragm,said assembly yfurther comprising a backing plate annularly connected I0said diaphragm only near the periphery of said diaphragm, with saidconductor film segments overlapping said backing plate, and conductoroutput leads conneet-ed to said output conductor segments externally ofsaid backing plate at about the peripheral edges of said diaphragm.

31. A [wafer type] pressure responsive assembly, comprising a pressuresensitive diaphragm, an electrically non-Conductive surface on saiddiaphragm and an electroconductive film pattern on said surface[diaphragm]` said film pattern comprising at least one active segmentsituated near-center of said diaphragm and at least one active segmentsituated near-edge of said diaphragm, such pattern further comprisingrelatively low resistance conductor segments integral with and extendingfrom juncture areas at the ends of said active segments to the peripheryof said diaphragm, a backing plate bonded to said diaphragm only nearthe edge thereof and contacting portions of said conductor filmsegments, conductor output leads connected to said output conductorsegments externally of said backing plate at about the peripheral edgesof said diaphragm, and bonding means between the periphery of saiddiaphragm and the outer portion of said backing plate retaining the sametogether and encapsulating the connections between said lm conductorsegments and said output leads.

32. An assembly according to claim 31, wherein said backing plate issubstantially more rigid than said dinphragm.

33. An assembly according to claim 31, wherein said diaphragm and saidbacking plate are formed of the same material.

34. An assembly according to claim 3l, wherein said diaphragm and saidbacking plate are of substantially the same thickness and have similarflexural characteristics, the ficxure of the backing plate thusaugmenting the pressure responsive flexural characteristics of saiddiaphragrn.

35. An assembly according to claim 34, wherein said diaphragm and saidbacking plate are fused silica.

36. An assembly according to claim 34, wherein said diaphragm and saidbacking plate are thin metal.

37. A [wafer type] pressure responsive assembly, comprising a pressuresensitive diaphragm having an electrica!- Iy non-conductive surface, andan electroconductive bridge pattern on said surface [diaphragml saidbridge `pattern comprising an integral film with at least one activesegment situated near-center of said diaphragm and at least one activefilm segment situated near-edge of said diaphragm, and with relativelylow resistance conductor segments integrally extending from about theradial stress null zone of said diaphragm to the periphery thereof, saidassembly further comprising a backing plate bonded to said diaphragm andto said conductor segments only near the outer edge of said diaphragm.

38. A [wafer type] pressure responsive assembly, comprising a pressuresensitive diaphragm having an electrically non-conductive surface, andan electroconductive bridge pattern on said surface [diaphragm], saidbridge pattern comprising an intergral iilrn with at least one activesegment situated near-center of said diaphragm and at least one activefilm segment situated near-edge of said diaphragm [diaphragm], and withrelatively low resistance conductor segments integrally extending fromabout the radial stress null zone of said diaphragm to the peripherythereof, a backing plate bonded to said diaphragm and said conductorsegments only near the outer extent thereof, conductor output leadsconnected to said output conductor segments externally of said backingplate at about the peripheral edge of said diaphragm, and thermosettingbonding means between the periphery of said diaphragm and the outerportion of said backing plate retaining the same together andencapsulating the connections between said conductor segments and saidoutput leads.

39. A strain sensitive [wafer type] pressure transducer assembly,comprising a flexible diaphragm having at least one electricallynon-conductive surface, and an integrally deposited film pattern n saidat least one surface of said diaphragm, said iilm pattern comprising twooppositely disposed active film segments situated within the radialstress null zone of said diaphragm and two oppositely disposed activefilm segments situated at least primarily in the area of the tangentialstress null zone of said diaphragm, such film pattern further comprisingrelatively low resistance output conductor film segments connecting withsaid active film segments in about the said radial stress null zone andextending outwardly therefrom to the periphery of said diaphragm, abacking plate bonded to said diaphragm and said conductor iilm segmentsonly near the outer extent thereof, conductor outputs leads connected tosaid output conductor segments externally of said backing plate at aboutthe peripheral edges of said diaphragm, and thermosetting bonding meansbetween the periphery of said diaphragm and the outer portion of saidbacking plate retaining the same together and encapsulating theconnections between said conductor film segments and said output leads.

40. [in a] A Wafer type pressure responsive device comprising [an edgeclamped] a exible diaphragm with means restraining the edge thereof,said diaphragm having an electrically non-conductive surfaces and anintegrally formed film pattern bonded to send [diaphragm] surfacesubstantially edge-to-edge of the diaphragm [and in essentially quadrantarrangement], said film pattern having at least one active segmentdisposed inside the radial stress null zone of said diaphragm and atleast one active film segment disposed outside the radial stress nullzone of said diaphragm, the thickness and length/width ratio of theactive film segments being substantially equal, and the active filmsegments being spaced substantially one from another so as to minimizeheating effects.

41. A transducer comprising a circular iiexible diaphragm with auelectrically non-conductive surface, means to [clamp] restrain saiddiaphragm near its peripheral edge, a bridge pattern including two pairsof active resistor segments bonded to said surface [diaphragml theresistor segments of a first pair being positioned on the said surfaceof said diaphragm near the [clamped] restrained edge of said diaphragm[thereofl the net stress in the diaphragm at said first pair of resistorsegments upon imposition of a uniform load being of net positive value,said first pair of resistor segments being symmetrically and oppositelyarranged on the diaphragm, the resistor segments of the second pair ofsegments being positioned adjacent to the center of the diaphragm, thenet stress in the diaphragm in the area of said second pair of resistorsegments being of negative value, said second pair of resistor segmentsalso being symmetrically and oppositely arranged on said diaphragm, saidbridge pattern further comprising junction areas interconnectingadjacent resistor segment ends, said juncture areas at least in partbeing in a region of the diaphragm where the factor r/a minus the factor[n+1 l2 [3mi-1 substantially equals zero, "r/u" being the distance "r ofsaid region from the center of the diaphragm divided by the radius "u ofthe diaphragm from the center to the restrained portion thereof, and rnbeing the reciprocals of the Poissons ratio of the diaphragm material.

42. A pressure responsive device comprising a pressure sensitivediaphragm with means restraining the edge thereof, said diaphragm havingan electrically non-conductive surface and a bridge pattern on saidsurface, said bridge pattern comprising at least two active segmentsterminating substantially in the radial stress null zone of thediaphragm, with one such active segment disposed near-center from theradial stress null zone of the diuphragm and the other such activesegment disposed nearedge from the radial stress null zone of thediaphragm.

43. A pressure responsive device comprising a pressure sensitivediaphragm with means restraining the edge thereof, said diaphragm havingan electrically' non-conductive surface and an integral bridge patternon said surface, said bridge pattern comprising at least two activesegments interconnetced at a juncture area lying .substatitially in theradial stress null zone of the diaphragm, with one such active segmentconnected to said juncture area disposed near-center from the radialstress null zone of the diaphragm and the other such active segmentconnected to said juncture area disposed near-edge from the radialstress null zone of the diaphragm.

44. A pressure responsive transducer comprising a ,h'exible diaphragmwith means restraining the edge thereof and With an electricallynon-conductive surface hav ing bonded thereon a bridge patterncomprising a plurality of active segments terminating at juncture areas,said pattern being arranged so that each of said juncture areas liessubstantially in the radial stress null zone of the diophragm, with onesuch active segment being disposed near-center from the radial stressnull zone of the diaphragm and the other active segment being disposednearedge from the radial stress null zone, of the diaphragm suchnear-edge active segment being disposed with a major part thereof in thearea of and near-edge with respect to the tangential stress null zolleof said' diaphragm.

45. A pressure responsive transducer comprising a flexible diaphragmwith means restraining the edge thereof and with an electricallynon-conductive surface having thereon a bonded bridge pattern in theform of an integral hlm, said bridge pattern comprising a plurality ofactive segments interconnected at juncture areas, said pattern beingarranged so that each of said juncture areas lies substantially in theradial stress null zone of thc diaphragm, with one active segmentconnected to euch such juncture arcas being disposed near-center fromthe radial stress null zone of the diaphragm and the other activesegment connected to each such juncture area being disposed near-edgefrom the radial stress null zone of the diaphragm, such near-edge activesegment being disposed with a major part thereof in the area of andnear-edge with respect to the tangential stress null zone of saiddiaphragm.

46. A pressure responsive device comprising a da phragm with meansrestraining the edge thereof und with an electrical/y non-coluluctivesurface having bonded thereto u bridge pattern comprising at least oneactive segment neor the center of the diaphragm and disposedsubstantially entirely in the region thereof where the distance/radiusratio is less than about 0.6, and further comprising at least one otheractive segment disposed substantially entirely in the region of thediaphragm where the distance/ radius ratio is at least about 0.7.

47. A pressure responsive device comprising a diaphragm with meansrestraining the edge thereof and with an electrically non-conductivesurface having an integral bridge pattern bonded thereto, said bridgepattern arrangement comprising at least one active segment near thecenter of tlze diaphragm substantially entirely in the region thereofwhere the distance/ radius ratio is less than about 0.6, and at leastone other active segment disposed substantially entirely in the regionof the diaphragm where the distance/radius ratio is at least about 0.7.

48. A pressure sensitive transducer comprising a circular flexiblediaphragm with means restraining the edge thereof and with anelectrically non-Conductive surface, a bridge pattern including aplurality of active resistor segments bonded to said surface, of which afirst resistor segment is positioned on the said surface near tlze edgeof said diaphragm, the net stress in the diaphragm in the area of saidjirst resistor segment upon imposition of a uniform load being of netpositive value, a second resistor segment positioned on said surfaceadjacent to the center of the diaphragm, the net stress in the diaphragmin the area of said second resistor segment being of negative value uponsuch uniform loading, said bridge pattern further comprising a juncturearea interconnecting adjacent ends of said hrst and second resistorsegments, said juncture area at least in part being in a region of thediaphragm where the factor r/ a minus tlze factor Stn-ll substantiallyequals zero, where "r/a is the distance "r" of said region from thecenter of the diaphragm divided by the radius "a of the diaphragm, and"m is the reciprocal of the Poissons ratio of the diaphragm material.

49. A flexible circular diaphragm adapted to act as a transduction meansin a transducer, comprising a circular flexible diaphragm rigidlyrestrained at its peripheral edge only, an electrically non-conductivesurface on said diaphragm, and a Jrlm pattern bonded to said surface,said film pattern including at least a pair of active segments, one ofsaid active segments being positioned entirely in and having terminalends positioned in the area of said diaphragm at a radial distanceequivalent to an r/a value substantially greater than about 0.6, andanother of said active elements being positioned entirely in and havingterminal ends positioned in the area of the diaphragm at a radialdistance equivalent to an r/a value substantially less than about 0.6,the said active segments being separated from each other by a radialdistance dijjerence extending a substantial distance both sides of aradial distance equivalent to an r/a value of about 0.6 where a" is theradius of said circular diaphragm and "r" is the above stated radialdistance, and relatively low electrical resistance juncture lms bondedto such diaphragm surface, one of said juncture films being connected toone of the terminal ends of each of the active segments of said pair.

50. A transduction element for a transducer comprising a circulardiaphragm rigidly restrained at its peripheral edge only, means to applya load to said diaphragm to deflect said diaphragm, an electricallynon-conductive surface on said diaphragm, and a film pattern bonded tosaid surface, said pattern including at least a pair of active segments,one of said active segments being positioned entirely in the area ofsaid diaphragm at a radial distance equivalent to an r/a value greaterthan about 0.6, and the other of said active segments being positionedentirely in the area of said diaphragm at a radial distance equivalentto an r/a value substantially less than about 0.6, with one of the saidactive segments being separated from the other of said active segmentsby a substantial radial distance difference, a plurality of junctureelements bonded to said diaphragm and interconnecting said activesegments', with each of said juncture elements extending a substantialdistance across a radial distance equivalent to an r/a value of about0.6 and a substantial distance to either side of said last named radialdistance, said juncture elements having a relatively low electricalresistance as compared with the electrical resistance of said activesegments, and electrical connectors connected to each of said junctureelements, where a" is a radius of the diaphragm and "r is said radialdistances.

5l. A transduction element for a transducer comprising a exible circulardiaphragm rigidly restrained at its peripheral edge only, anelectrically non-conductive surface on said diaphragm, and a filmpattern bonded to said surface, said pattern including at least twopairs of active segments, the active segments of one of said pairs beingseparated from each other and bei/tg positioned entirely in the area ofsaid diaphragm at a radial distance equivalent to an r/a valuesubstantially greater than about 0.6, said active segments terminatingat a radial distance equivalent to an r/a value substantially greaterthan about 0.6, and the active segments of the other of said pairs beingseparated from each other and being positioned entirely in the area ofthe diaphragm at a radial distance substantially less than thatequivalent to an. r/a value of about 0.6, said last named activesegments terminating at a radial distance equivalent to an r/ a value ofsubstantially less than about 0.6, the said active segments of one ofsaid pairs being separated from the active segments of the other of saidpairs, and the ends of the segments of one of said pairs being separatedfrom the ends of the other active segments of the other of said pairs bya radial distance dijjerence extending a substantial radial distanceboth sides of a radial distance equivalent to an r/a value of about 0.6,where a is the radius of the diaphragm and r is the above radialdistances, each such end of said active segments of one of said pairsbeing connected to an associated terminal end of an active segment ofthe other of said pairs by a junction film bonded to said diaphragm,each said junction film having a relatively low electrical resistancecompared to the resistance of said active segments and electricallyconnecting said active segments in a bridge configuration, with saidactive segments being otherwise electrically insulated from eac/i otherexcept at such junctions.

References Cited by the Examiner The following references, cited by theExaminer, are of record in the patented le of this patent or theoriginaI patent.

UNITED STATES PATENTS 2,318,102 5/1943 Ruge 338-2 2,848,892 8/1958Hoffman 73-141 3,049,685 8/1962 Wright 73-885 X 3,079,576 2/1963 Kooiman338-4 3,122,717 2/1964 Motsinger 338-4 ANTHONY BARTIS, Acting PrimaryExaminer.

RICHARD M. WOOD, Examiner.

W. D. BROOKS, Assistant Examiner.

